A congressional panel investigating the US Capitol attack has subpoenaed Donald Trump’s White House counsel to testify about the former US president’s activities on the day of the melee.

The subpoena seeking a deposition from Pat Cipollone followed dramatic public testimony on Tuesday from a former White House aide, who told the panel that Mr Cipollone had warned her they could face “every crime imaginable” if Mr Trump went to the Capitol on January 6, 2021, after delivering a fiery rally speech to his supporters.

“The select committee’s investigation has revealed evidence that Mr Cipollone repeatedly raised legal and other concerns about President Trump’s activities on January 6th and in the days that preceded,” the panel said on Wednesday (US time).

“Any concerns Mr Cipollone has about the institutional prerogatives of the office he previously held are clearly outweighed by the need for his testimony,” the committee said.

Mr Cipollone could not be reached immediately for comment.

Cassidy Hutchinson, an aide to Mr Trump’s White House chief of staff Mark Meadows, told the committee on Tuesday that Mr Trump wanted to leave the rally for the Capitol and that he grabbed the steering wheel of the presidential limousine when he learned the Secret Service would not drive him to there, where thousands of his supporters were rioting.

“We’re going to get charged with every crime imaginable,” Ms Hutchinson said Mr Cipollone told her if Mr Trump were to go to the Capitol on January 6.

“‘We need to make sure that this doesn’t happen, this would be a really terrible idea for us. We have serious legal concerns if we go up to the Capitol that day,'” Mr Cipollone said, according to Ms Hutchinson’s testimony.

But the probe faced questions on Wednesday about what steps it had taken to corroborate Ms Hutchinson’s account of Mr Trump’s having struggled with Secret Service agents.

Ms Hutchinson testified that Tony Ornato, a senior Secret Service official, told her that Mr Trump, a Republican, had struggled with agents after giving a fiery speech to his supporters outside the White House that morning, in which he repeatedly falsely blamed widespread fraud for his election loss to Democrat Joe Biden.

US media outlets, citing Secret Service sources, said the head of Mr Trump’s security detail, Robert Engel, and the car’s driver were prepared to challenge Ms Hutchinson’s testimony that Mr Trump had tried to grab the steering wheel.

Mr Trump has denied having grabbed the wheel.

An aide to the US House of Representatives committee declined to answer questions about whether it already had interviewed Secret Service agents or other officials with firsthand knowledge of the incident Ms Hutchinson described.

“Ms Hutchinson stands by all of the testimony she provided yesterday, under oath, to the Select Committee to Investigate the January 6th Attack on the United States Capitol,” her lawyers Jody Hunt and William Jordan said in a statement.

A Secret Service spokesman said the committee had not sought to confirm details of Ms Hutchinson’s testimony before the hearing, which was scheduled unusually quickly.

The riot was an attempt to stop Congress, with then vice-president Mike Pence presiding, from certifying Mr Biden’s election.

Supporters of Mr Trump have not challenged other revelations in Hutchinson’s testimony.

These included Mr Trump’s knowledge – even approval – of his supporters’ walking around Washington heavily armed on January 6 and that he had no qualms about rioters’ urging that Mr Pence be hanged.

Ms Hutchinson also testified that Mr Trump was known for angry outbursts in the White House that left food splayed onto walls and dishes upended.

– AAP